Conductive metal oxide structures in non-volatile re-writable memory devices

ABSTRACT

A memory cell including a memory element comprising an electrolytic insulator in contact with a conductive metal oxide (CMO) is disclosed. The CMO includes a crystalline structure and can comprise a pyrochlore oxide, a conductive binary oxide, a multiple B-site perovskite, and a Ruddlesden-Popper structure. The CMO includes mobile ions that can be transported to/from the electrolytic insulator in response to an electric field of appropriate magnitude and direction generated by a write voltage applied across the electrolytic insulator and CMO. The memory cell can include a non-ohmic device (NOD) that is electrically in series with the memory element. The memory cell can be positioned between a cross-point of conductive array lines in a two-terminal cross-point memory array in a single layer of memory or multiple vertically stacked layers of memory that are fabricated over a substrate that includes active circuitry for data operations on the array layer(s).

FIELD

The present invention relates generally to data storage technology. Morespecifically, the present invention relates to non-volatile re-writeablememory.

BACKGROUND

Data retention is a characteristic by which to measure the effectivenessof memory cells to ensure non-volatility of data stored therein. Avariety of conventional memory cells structures have been developed toenhance data retention for various memory technologies, many of whichare not well-suited to enhancing data retention in non-volatilere-writable memory cells including conductive oxide-based memorystructures.

There are continuing efforts to improve non-volatile re-writable memorytechnologies.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its various embodiments are more fully appreciated inconnection with the following detailed description taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 depicts a cross-sectional view and a schematic view of a memorycell according to various embodiments of the invention;

FIG. 1A depicts a cross-sectional view of ion motion in response to aprogramming voltage applied across a memory cell;

FIG. 1B depicts a cross sectional view and a schematic view of a memorycell after a programming voltage has been applied;

FIG. 1C depicts a cross-sectional view of ion motion in response to anerase voltage applied across a memory cell;

FIG. 1D depicts a cross sectional view and a schematic view of a memorycell after an erase voltage has been applied;

FIG. 2A depicts an example of a memory cell that includes a pyrochloreoxide material according to at least some embodiments of the invention;

FIG. 2B depicts a memory cell implementing a conductive binary oxideaccording to at least some embodiments of the invention;

FIG. 3A depicts one example of a memory cell implemented using aconductive binary oxide according to various embodiments of theinvention;

FIG. 3B depicts another example of a memory cell implemented using aconductive binary oxide according to various embodiments of theinvention;

FIG. 3C depicts yet another example of a memory cell implemented using aconductive binary oxide according to various embodiments of theinvention;

FIG. 4 depicts a memory cell implementing non-perovskite ornon-traditional perovskite conductive metal oxides according to variousembodiments of the invention;

FIG. 5A depicts an example of a memory cell implementing anon-traditional multiple B-site perovskite conductive metal oxideaccording to various embodiments of the invention;

FIG. 5B depicts an example of a memory cell implementing aRuddlesden-Popper conductive metal oxide according to variousembodiments of the invention;

FIG. 6 depicts an example of memory cells positioned in a two-terminalcross-point array according to various embodiments of the invention;

FIG. 6A depicts one example of a memory cell that includes a memoryelement electrically in series with a non-ohmic device;

FIG. 6B depicts another example of a memory cell that includes a memoryelement electrically in series with a non-ohmic device;

FIG. 6C depicts a memory cell positioned between a cross-point of twoconductive array lines;

FIG. 6D depicts a plurality of memory cells including memory elementwith continuous and unetched layers and positioned between cross-pointsof conductive array lines;

FIG. 7 depicts an integrated circuit including memory cells disposed ina single memory array layer or in multiple memory array layers andfabricated over a substrate that includes active circuitry fabricated ina logic layer;

FIG. 8A depicts a cross-sectional view of an integrated circuitincluding a single layer of memory fabricated over a substrate includingactive circuitry fabricated in a logic layer;

FIG. 8B depicts a cross-sectional view of an integrated circuitincluding vertically stacked layers of memory fabricated over asubstrate including active circuitry fabricated in a logic layer;

FIG. 8C depicts a vertically stacked layers of memory in whichconductive array lines are shared by memory cells in adjacent layers;

FIG. 8D depicts an integrated circuit including vertically stackedlayers of memory with shared conductive array lines fabricated over asubstrate including active circuitry fabricated in a logic layer;

FIG. 9 depicts a memory system including a non-volatile two-terminalcross-point array;

FIG. 10 depicts an exemplary electrical system that includes at leastone non-volatile two-terminal cross-point array; and

FIG. 11 depicts top plan views of a wafer processed FEOL to form aplurality of base layer die including active circuitry and the samewafer subsequently processed BEOL to form one or more layers of memorydirectly on top of the base layer die where the finished die cansubsequently be singulated, tested, and packaged into integratedcircuits.

Although the above-described drawings depict various examples of theinvention, the invention is not limited by the depicted examples. It isto be understood that, in the drawings, like reference numeralsdesignate like structural elements. Also, it is understood that thedrawings are not necessarily to scale.

DETAILED DESCRIPTION

Various embodiments or examples of the invention may be implemented innumerous ways, including as a system, a process, an apparatus, or aseries of program instructions on a computer readable medium such as acomputer readable storage medium or a computer network where the programinstructions are sent over optical, electronic, or wirelesscommunication links. In general, operations of disclosed processes maybe performed in an arbitrary order, unless otherwise provided in theclaims.

A detailed description of one or more examples is provided below alongwith accompanying figures. The detailed description is provided inconnection with such examples, but is not limited to any particularexample. The scope is limited only by the claims, and numerousalternatives, modifications, and equivalents are encompassed. Numerousspecific details are set forth in the following description in order toprovide a thorough understanding. These details are provided as examplesand the described techniques may be practiced according to the claimswithout some or all of the accompanying details. For clarity, technicalmaterial that is known in the technical fields related to the exampleshas not been described in detail to avoid unnecessarily obscuring thedescription.

U.S. patent application Ser. No. 11/095,026, filed Mar. 30, 2005, nowU.S. Published Application No. 2006/0171200 A1, and entitled “MemoryUsing Mixed Valence Conductive Oxides,” is hereby incorporated byreference in its entirety for all purposes and describes non-volatilethird dimensional memory elements that may be arranged in atwo-terminal, cross-point memory array. New memory structures arepossible with the capability of this third dimensional memory array. Inat least some embodiments, a two-terminal memory element or memory cellcan be configured to change conductivity when exposed to an appropriatevoltage drop across the two-terminals. The memory element can include anelectrolytic tunnel barrier and a mixed valence conductive oxide in someembodiments, as well as multiple mixed valence conductive oxidestructures in other embodiments. A voltage drop across the electrolytictunnel barrier can cause an electrical field within the mixed valenceconductive oxide that is strong enough to move oxygen ions out of amixed valence conductive oxide, according to some embodiments.

In some embodiments, an electrolytic tunnel barrier and one or moremixed valence conductive oxide structures do not need to operate in asilicon substrate, and, therefore, can be fabricated above circuitrybeing used for other purposes. Further, a two-terminal memory elementcan be arranged as a cross point such that one terminal is electricallycoupled with an X-direction line (or an “X-line”) and the other terminalis electrically coupled with a Y-direction line (or a “Y-line”). A thirddimensional memory can include multiple memory cells vertically stackedupon one another, sometimes sharing X-direction and Y-direction lines ina layer of memory, and sometimes having isolated lines. When a firstwrite voltage, VW1, is applied across the memory cell (e.g., by applying½ VW1 to the X-direction line and ½-VW1 to the Y-direction line), thememory cell can switch to a low resistive state. When a second writevoltage, VW2, is applied across the memory cell (e.g., by applying ½ VW2to the X-direction line and ½-VW2 to the Y-direction line), the memorycell can switch to a high resistive state. Memory cells usingelectrolytic tunnel barriers and mixed valence conductive oxides canhave VW1 opposite in polarity from VW2.

FIG. 1 depicts a memory element for implementation in a memory array,according to various embodiments of the invention. In this example,memory cell 100 is depicted to include a first terminal 104 and a secondterminal 106. As used herein, the term “memory cell” can refer, at leastin some embodiments, to various layers of materials, including memorymaterial(s), arranged between conductive lines (e.g., conductive arraylines in a cross-point array). The various layers of materials can alsoinclude a top terminal (or electrode) and a bottom terminal (orelectrode). Furthermore, some or all of the layers of material may bepatterned (i.e., discrete etched layers) or a portion of the layers maybe continuous (e.g., un-etched layers) across a plurality of adjacentmemory cells as disclosed in U.S. Pat. No. 7,742,323, issued on Jun. 22,2010, and titled “Continuous Plane Of Thin-Film Materials For ATwo-Terminal Cross-Point Memory”, which is incorporated herein byreference in its entirety for all purposes. In FIG. 1, the layers 110and 120 may be discrete layers that have been deposited as a thin filmand subsequently etched to form discrete layers depicted or the layers110 and 120 may be continuous layers that are not etched as will bedescribed below in reference to FIG. 6D. Memory cell 100 includes aconductive metal oxide (CMO) 110 and an electrolytic insulator 120 incontact with and electrically in series with the CMO 110. The CMO 110and the electrolytic insulator 120 are electrically in series with thefirst terminal 104 and the second terminal 106. As will be describedbelow, the terminals 104 and 106 may represent one or more electricallyconductive structures operative to electrically communicate voltages fordata operations to the memory cell 100, including but not limited toelectrodes, glue layers, adhesion layers, and portions of conductivearray lines, for example. In various embodiments, electrolytic insulator120 can be formed either above or below CMO 110. In at least someembodiments, electrolytic insulator 120 is an electronic insulator andan ionic electrolyte, as a medium, that provides an ion transportmechanism between positive and negative potentials applied to terminals104 and 106. In at least some embodiments, electrolytic insulator 120can be an electrolytic tunnel barrier layer configured to provide fortunneling, which can include, but is not limited to, single steptunneling processes (e.g., direct tunneling, Fowler-Nordheim tunneling,and thermionic field emission tunneling), multi-step tunneling processes(e.g., trap-assisted tunneling), and the like. The electrolyticinsulator 120 can be made from materials including but not limited torare earth oxides, rare earth metal oxides, yttria stabilized zirconia(YSZ), yttrium oxide (Y₂O₃), zirconium oxide (ZrO_(X)), also referred toas zirconia (e.g., ZrO₂), hafnium oxide (HfO_(X)), gadolinium oxide(GdO_(X)), lanthanum aluminum oxide (LaAlO_(X)), erbium oxide (ErO_(X))(e.g., Er₂O₃), and the like.

Electrolytic insulator 120 can be configured to accumulate ions, and CMO110 can be configured to serve as an ion supply. Accordingly, CMO 110includes mobile ions 114 that can be transported from the CMO 110 to theelectrolytic insulator 120 in response to a first electric field (notshown) of sufficient magnitude and transported back from theelectrolytic insulator 120 to the CMO 110 in response to a secondelectric field (not shown) of sufficient magnitude as will be describedbelow. The electrolytic insulator 120 can include interstitial sites orvacancies 112 (vacancies 112 hereinafter) operative to receive mobileions 114 that are transported into the electrolytic insulator 120 inresponse to the first electric field. The number of mobile ions 114 andvacancies 112 will not be necessarily be equal and will depend in parton the materials selected, their thickness, just to name a few. As oneexample, the mobile ions may be oxygen (O⁻) ions that have a negativecharge. CMO 110 includes a thickness t_(c) and electrolytic insulator120 includes a thickness t_(i). Actual values for the thicknesses willbe application dependent; however, for tunneling to occur at voltagelevels that can be generated by circuitry (e.g., CMOS technology)operative for data operations to the memory cell 100 (e.g., read andwrite operations), the thickness t_(i) will be approximately 50 Å orless. Typically, thickness t_(i) is substantially less than thethickness t_(c) (e.g., t_(i)<<t_(c)). For example, thickness t_(i) canbe in a range from about 5 Å to about 35 Å and thickness t_(c) can be ina range from about 100 Å to about 350 Å. Preferably, thickness t_(c) isless than about 100 Å. In FIG. 1, the memory cell 100 is operative tostore data as a plurality of conductivity profiles that can benon-destructively determined by applying a read voltage across theterminals 104 and 106. The application of the read voltage generates aread current and a magnitude of the read current is indicative of thevalue of the stored data. The conductivity profiles can representresistive states that can be reversibly switched by applying a writevoltage across the terminals 104 and 106. For example, a high value ofresistance can represent a logic “0” (e.g., a programmed state≈1 MΩ) anda low value of resistance can represent a logic “1” (e.g., an erasedstate≈100 kΩ). For purposes of illustration, the memory cell may beelectrically modeled as a variable resistance 100 r having a resistanceR_(S) that can be reversibly modulated up and down U/D by write voltageshaving sufficient magnitude and polarity that are applied acrossterminals 104 and 106. The write voltage generates an electric field inlayers 110 and 120 operative to move the ions 114 from the CMO 110 tothe insulator 120 or from the insulator 120 to the CMO 110. Therefore,the movement of ions between electrolytic insulator 120 and CMO 110 canmodify the electronic conductivity profile of CMO 110 by eitherincreasing electronic conductivity as a function of the ionic conductionin one direction, or decreasing electronic conductivity as a function ofthe ionic conduction in another direction. For example, ion conductioncan cause the electronic conductivity of CMO 110 to either increase ordecrease in terms of the values of conductivity. In at least someembodiments, CMO 110 can include non-perovskite structures (e.g., aRuddlesden-Popper structure). In at least some embodiments, CMO 110 caninclude a non-traditional perovskite structure (e.g., a multiple B-siteperovskite structure). In at least some embodiments, CMO 110 can includeconductive binary oxide structures. In at least some embodiments, CMO110 can include pyrochlore oxide structures. The CMO 110 can have acrystalline structure or an amorphous structure. Examples of crystallinestructures for the CMO 110 include but are not limited to a singlecrystalline structure, a polycrystalline structure, a multi-phasecrystalline structure, a mixed-phase crystalline structure, a columnarcrystalline structure, and a micro crystalline structure.

In view of the foregoing, the structures and/or functionalities ofmemory cell 100 can enhance data retention, among other things. In atleast some embodiments, CMO 110 can provide for a mechanism by whichconductivity modification in memory cell 100 can occur separate from, orin addition to, a conductivity modification mechanism provided with theinteraction of electrolytic insulator 120. In at least some embodiments,ionic conduction may or may not be complemented by electron conduction,whereby holes and electrons (e.g., electron-hole pairs) move withinmemory cell 100 to facilitate conductivity modification of memory cell100. These conduction mechanisms, in turn, can increase a sensing windowwith which to read data (or a datum) stored in memory cell 100.

In at least some embodiments, CMO 110 can be formed from a materialhaving a conductivity σ that may be proportional to a quantity q of ionsI (e.g., q(I)) in CMO 110, such that σ≈f(q(I)). The term “ions” in thecontext of “quantity of ions” can generally refer, at least in someembodiments, to ions that are available to participate in ionicconduction, such as mobile ions 114. In operation, a potentialdifference applied across terminal 104 and terminal 106 can give rise toan electric field in a first direction. In this case, the electric fieldpromotes ionic conduction such that ions 114, which can be described asmobile ions, are transported in a direction that moves ions from CMO 110to electrolytic insulator 120 (e.g., ions 114 move into ion vacancies112). Under the electric field in the first direction, ions 114 aretransported to ion vacancies 112 in electrolytic insulator 120. As ions114 leave CMO 110 and ion vacancies 112 are filled in electrolyticinsulator 120, the electronic conductivity of CMO 110 decreases. Ionicconduction in this direction (i.e., a direction of travel that isopposite that of the electric filed in the first direction) facilitatestransitioning CMO 110 to an ion-deficient state, as well astransitioning electrolytic insulator 120 to an accumulated ion state(e.g., an ion-rich state).

Conversely, another potential difference applied between terminal 104and terminal 106 can give rise to an electric field in a seconddirection. In this case, the electric field promotes ionic conductionsuch that ions are transported in a direction that moves ions fromelectrolytic insulator 120 to CMO 110. For example, under the electricfield in a second direction, ions 114 that occupy vacancies 112 inelectrolytic insulator 120 are transported to ion vacancies that werecreated in CMO 110 by the departure of the ion 114. As ions 114 leaveelectrolytic insulator 120 and return to CMO 110, the quantity of ions114 entering the CMO 110 can cause the conductivity to increase. Thus,ionic conduction in this direction (e.g., direction of travel that isopposite the electric field in the second direction) facilitatestransitioning CMO 110 out of an ion-deficient state, as well astransitioning electrolytic insulator 120 out of an accumulated ionstate. In some embodiments, the aforementioned potential differences canbe implemented to program and erase data (or a datum) in memory cell100. Other potential differences can be applied, such as during a readoperation, that are different than the aforementioned potentialdifferences (e.g., read voltages having magnitudes that are less thanwrite voltages used to program or erase the memory cell 100), and arenon-destructive to data previously stored in memory cell 100.

Reference is now made to FIG. 1A where a configuration 150 depicts avoltage source 125 electrically coupled (102, 103) with terminals (104,106) via a switch 130 depicted as being closed so that a programmingvoltage V_(P) is applied across the terminals (104, 106). Theprogramming voltage V_(P) may be applied as a voltage pulse 135.Although a single voltage source 125 is depicted, the programmingvoltage V_(P) may be applied by separate voltage sources, oneelectrically coupled with terminal 104 and the other electricallycoupled with terminal 106. The voltage source(s) and associatedcircuitry and interconnect structures may be positioned on a substratethe memory cell 100 is fabricated over. A magnitude and polarity of theprogramming voltage V_(P) is operative to generate a first electricfield E₁ in a direction depicted by a dashed arrow. For purposes ofexplanation, assume mobile ions 114 are negatively charged so that inresponse to the first electric field E₁, at least a portion of the ions114 in CMO 110 are transported 118 to the electrolytic insulator 120where at least a portion of those ions 114 enter vacancies 112.

Turning now to FIG. 1B, a configuration 151 depicts the switch 130 asopen such that the programming voltage V_(P) is no longer applied acrossterminals (104, 106). The transport of ions 114 from CMO 110 has createdvacancies 124 in the CMO 110, Furthermore, vacancies 112 in theelectrolytic insulator 120 that received the mobile ions 114 have becomeoccupied vacancies 122. As was described above, the transport of theions 114 creates an ion deficient state in the CMO 110 that changes theconductivity profile of the CMO 110. Here, the electrical model forvariable resistance 100 r models the ion deficient state as a decreasein conductivity of the CMO 110 such that the resistance R_(S) (seeFIG. 1) is modulated upward and increases to a resistance R_(P)indicative of the programmed state of memory cell 100 (e.g., a highresistance in the programmed state).

Moving on to FIG. 1C, a configuration 153 depicts a voltage source 127electrically coupled (102, 103) with terminals (104, 106) via a switch139 depicted as being closed such that an erase voltage V_(E) is appliedacross the terminals (104, 106). The erase voltage V_(E) may be appliedas a voltage pulse 137. A magnitude and polarity of erase voltage V_(E)is operative to generate a second electric field E₂ that is opposite indirection to the first electric field E₁ (see FIG. 1A). In response tothe second electric field E₂, at least a portion of the mobile ions 114positioned in occupied vacancies 122 are transported 119 back to the CMO110 and into vacancies 124.

Referring now to FIG. 1D, a configuration 155 depicts the switch 139 asopen such that the erase voltage V_(E) is no longer applied acrossterminals (104, 106). The transport 119 of the ions 114 back into theCMO 110 has transitioned the CMO 110 from the ion deficient state ofFIG. 1B to an ion rich state. Consequently, changing the conductivityprofile of memory cell 100. Here, the electrical model for variableresistance 100 r models the ion rich state as an increase inconductivity of the CMO 110 such that the resistance R_(S) (see FIG. 1)is modulated downward and decreases to a resistance R_(E) indicative ofthe erased state of memory cell 100 (e.g., a low resistance in theerased state).

As will be described in greater detail below, one criteria for selectingthe materials for the CMO 110 and the electrolytic insulator 120 is dataretention, that is, a measure of the ability of the memory cell 100 toretain stored data over time, such that conductivity values that areindicative of stored data do not substantially drift over time and thestored data can be reliably read during a read operation. Anothercriteria is memory effect, a measure of the difference in read currentmagnitudes for different states of stored data (e.g., a logic “0” vs. alogic “1”). The larger the difference, the easier it is for sensecircuitry to accurately determine if data read is indicative of thememory cell 100 being in a programmed state or an erased state.Essentially, the larger the difference, the higher the signal-to-noiseratio (S/N). In regards to FIG. 1B, data retention can be explained asthe ions 114 remaining in occupied vacancies 122 in the absence of power(e.g., a write voltage applied across terminals 104 and 106) and when aread voltage is applied across terminals 104 and 106. Typically, amagnitude of the read voltage is less than a magnitude of the writevoltage (e.g., V_(P) and V_(E)). Accordingly, a magnitude of an electricfield generated by the read voltage is insufficient to transport theions 114 from their respective occupied vacancies 122 and resistanceR_(P) does not change over time. Similarly, in regards to FIG. 1D, dataretention can be explained as the ions 114 remaining in CMO 110 in theabsence of power and when the read voltage is applied across terminals104 and 106. Consequently, resistance R_(E) does not change over time.

Reference is now made to FIG. 2A which depicts an example of a memorycell 200 that includes a pyrochlore oxide material 210 as the conductivemetal oxide, according to at least some embodiments of the invention. Asshown, FIG. 2A depicts an electrolytic insulator 220 and a pyrochloreoxide material 210 as the conductive metal oxide 110 of FIG. 1. The CMOfor the layer 210 crystallizes in a pyrochlore oxide structure, alsoreferred to as a pyrochlore oxide phase. For example, the layer 210 canhave a crystalline structure. Both electrolytic insulator 220 and thepyrochlore oxide material 210 are in contact with each other and areelectrically in series with each other and with the terminals 104 and106. Pyrochlore oxide material 210 can have an oxygen-deficient stateand can be configured to promote ion conduction by, for example, usingdopants that facilitate conduction of oxygen ions 214. As used herein,the term “pyrochlore material” can refer, at least in some embodiments,to metal oxides having a structure that is the same as or is similar tothe mineral pyrochlore, and/or can be described as having the generalform A₂B₂O₇, or any variants thereof. The A and B sites generallyinclude, for example, rare-earth or transition metal elements, and Orepresents oxygen. As one example, A can represent at least one elementincluding but not limited to a rare earth element, barium (Ba),strontium (Sr), lead (Pb), bismuth (Bi), and potassium (K). As anotherexample, B can represent a rare earth element or a transition metalelement. As was described above, the first electric field E₁ can beoperative to transport the mobile oxygen ions 214 to electrolyticinsulator 220 where those ions occupy vacancies 212. The second electricfield E₂ can be operative to transport the mobile oxygen ions 214 fromoccupied vacancies (not shown) in the electrolytic insulator 220 backinto vacancies (not shown) in the pyrochlore oxide material 210. Thethickness t_(i) and t_(c) for the layers 220 and 210 respectively, willbe application dependent.

Moving on to FIG. 2B, a memory cell 201 implementing a conductive binaryoxide as an example of the CMO 110 of FIG. 1 is depicted, according toat least some embodiments of the invention. In this example, memory cell201 includes a conductive binary oxide structure 230 (e.g., as an ionreservoir) in contact with an electrolytic insulator 220 and disposedbetween terminals 104 and 106, across which potential differences can beapplied. The conductive binary oxide structure 230 and the electrolyticinsulator 220 are electrically in series with each other and theterminals 104 and 106. Conductive binary oxide structure 230 can be anymetal oxide having the form A_(X)O_(Y), where A represents a metal and Orepresents oxygen. The conductive binary oxide structure 230 may bedoped to obtain the desired conductive properties for a CMO. Forexample, depending on the material selected for the layer 230, elementsincluding but not limited to niobium (Nb), fluorine (F), and nitrogen(N) can be used as dopants to alter the conductivity of the layer 230.As one example, doping can be accomplished using a co-sputtering processthat is well understood in the microelectronics art. In at least oneembodiment, conductive binary oxide structure 230 has a conductivitythat is lower in an oxygen-deficient state. In at least someembodiments, the conductivity of conductive binary oxide structure 230can be configured to promote electronic conduction (e.g., electron-holepair movement) in addition to ionic conduction of oxygen ions 234. Theelectrolytic insulator 220 can be made from materials including but notlimited to an electrically insulating high-k dielectric material, rareearth oxides, rare earth metal oxides, yttria stabilized zirconia (YSZ),yttrium oxide (Y₂O₃), zirconium oxide (ZrO_(X)), also referred to aszirconia (e.g., ZrO₂), hafnium oxide (HfO_(X)), gadolinium oxide(GdO_(X)), erbium oxide (ErO_(X)) (e.g., Er₂O₃), and the like. As wasdescribed above, electrolytic insulator 220 includes vacancies 212. Inat least one embodiment, a conductive binary oxide structure 230 can beformed directly in contact with a YSZ structure as electrolyticinsulator 220. In view of the foregoing, conductive binary oxidestructure 230 can be implemented as a source of ions to promoteconduction (e.g., ionic and/or electronic) rather than otherwise mightbe the case (e.g., such as using a conductive binary oxide as aninsulator to reduce and/or inhibit conduction). The conductive binaryoxide structure 230 includes a crystalline structure.

FIGS. 3A through 3C depict examples of memory cells implementingconductive binary oxides as the CMO 110 of FIG. 1, according to variousembodiments of the invention. In the example shown in FIG. 3A, a memorycell 300 includes an electrolytic insulator 320 and a tin oxide(SnO_(X)) (e.g., SnO₂) material 310 as a conductive binary oxidestructure, both electrolytic insulator 320 and tin oxide material 310are in contact with and electrically in series with each other and aredisposed between terminals 104 and 106 and are electrically in serieswith terminals 104 and 106. In the examples shown in FIGS. 3B through3E, memory elements 301 and 307 include a zinc oxide (ZnO_(X)) (e.g.,ZnO₂) material 330 and a doped titanium oxide (TiO_(X)) (e.g., TiO₂)material 370, respectively, as conductive binary oxide structures thatare in contact with and electrically in series with their respectiveelectrolytic insulator layers 320 and are disposed between terminals 104and 106 and electrically in series with those terminals. As wasdescribed above in reference to FIGS. 1A through 1D, the application ofvoltage V_(P) is operative to transport mobile ions (not shown) fromconductive binary oxide CMO layers 310, 330, and 370 and into theirrespective electrolytic insulator layers 320 and the application ofvoltage V_(E) is operative to move the mobile ions from the vacanciesthey occupied in the electrolytic insulator layer 320 and back into theCMO layers 310, 330, and 370. In FIG. 3C, the titanium oxide (TiO_(X))material 370 can be doped with a material including but not limited toniobium (Nb). The doping of the titanium oxide (TiO_(X)) can beaccomplished by a process including but not limited to co-sputteringduring deposition of the layer 370.

FIG. 4 depicts a memory cell 400 implementing either a non-perovskiteconductive metal oxide or a non-traditional perovskite conductive metaloxide as an example of the CMO 110, according to at least someembodiments of the invention. In this example, the memory cell 400includes a CMO structure 410 (e.g., as a reservoir for mobile ions 414)in contact with and electrically in series with an electrolyticinsulator 420. The electrolytic insulator 420 includes vacancies as wasdescribed above in reference to FIGS. 1-1D. The layers 410 and 420 aredisposed between and are electrically in series with terminals 104 and106, across which the aforementioned potential differences (e.g., V_(P),V_(E), and read voltages) can be applied. The CMO for the structure 410can include a non-traditional multiple B-site perovskite or aRuddlesden-Popper structure as will be described below in reference toFIGS. 5A and 5B. The thicknesses t_(c) and t_(i) will be applicationdependent. As one example, thickness t_(c) for layer 410 can be fromabout 100 Å to about 350 Å and thickness t_(i) for layer 420 can be fromabout 10 Å to about 35 Å.

FIGS. 5A and 5B depict examples of memory cells implementing additionaltypes of conductive metal oxides for the layer 410 of FIG. 4, accordingto various embodiments of the invention. In the example depicted in FIG.5A, memory cell 500 includes an electrolytic insulator 520 and amultiple B-site Perovskite oxide material 510 as the structure 410 ofFIG. 4. Specifically, multiple B-site Perovskite oxide material 510 canbe formed to include two or more elements at the B sites in the unitcells of a perovskite structure. Multiple B-site Perovskite oxidematerial 510 can be represented as having the form A_(X)(B₁,B₂)_(Y)O_(Z), where A represents a site at which one or more elementscan be disposed, B₁ and B₂ represents at least two elements located atthe B-sites of a perovskite structure, where the element for the B₁ siteis different than the element for the B₂ site. For example, the multipleB-site perovskite material 510 includes the perovskite unit cellstructure with each unit cell having a B-site. Some portion of theB-sites in the unit cells will have the B₁ element and another portionof the B-sites in the unit cells will have the B₂ element. The number ofunit cells having the B₁ element at their respective B-sites may not beequal to the number of unit cells having the B₂ element at theirrespective B-sites. As another example, in the layer 510, one unit cellmay have a B₁ element at its B-site and an adjacent unit cell may have aB₂ element at its B-site. Therefore, throughout the layer 510, some unitcells have the B₁ element at their B-sites and other unit cells have theB₂ element at their B-sites. In the multiple B-site Perovskite oxidematerial 510, O represents oxygen, where Z typically is 3, X can be anynumber, and Y typically is 1. In at least some embodiments, cobaltitesand ferrites can be disposed at the B sites (i.e., the elements cobalt(Co) and iron (Fe)). An example of multiple B-site Perovskite oxidematerial 510 can be described as (LaSr)(CoFe)O₃, where the La and Srelements are disposed at the A-sites and the Co and Fe elements aredisposed at the B-sites, B₁ and B₂ respectively. In various embodiments,B₁ and B₂ elements can include one or more elements from the transitionmetals, with the element for B₁ being different than the element for B₂.

FIG. 5B depicts a memory cell 503 implementing a Ruddlesden-Popperstructure conductive metal oxide for the layer 410 of FIG. 4, accordingto various embodiments of the invention. In the example shown, thememory cell 503 includes an electrolytic insulator 520 and aRuddlesden-Popper structure 540. In some embodiments, Ruddlesden-Popperstructure 540 can be a perovskite of, for example, a type ABO₃. In someembodiments, Ruddlesden-Popper structure 540 can be formed as aRuddlesden-Popper type oxide that can generally be described as havingthe form AO(ABO₃)_(n), or any variants thereof, where n represents aRuddlesden-Popper phase. In some cases, the A sites can include elementsfrom the alkaline earth metals, and the B sites can include elementsfrom the transition metal elements. As an oxide, Ruddlesden-Popperstructure 540 can have an oxygen-deficient state and can be configuredto promote ion conduction by, for example, using dopants that facilitateoxygen ion conduction.

One advantage of the non-perovskite and non-traditional perovskite CMO'sdescribed herein is that the materials for the CMO 110 are selected tomeet at least two conductive properties that can be tailored to providedesired device performance criteria: (1) the material selected for theCMO 110 is electronically conductive to generate sufficient currentcreated by electron and/or hole motion; and (2) the material selectedfor the CMO 110 is ionically conductive to provide sufficient ioncurrent (e.g., via mobile ions 114) that is responsive to the first andsecond electric fields (E₁, E₂) that are generated by the voltages(e.g., V_(P) and V_(E)) applied across the terminals (104, 106).Depending on factors including but not limited to the material selectedfor the CMO 110 (e.g., the CMO's depicted in FIGS. 2A-5B), thethicknesses t_(c) and t_(i), properties (1) and (2) can be balanced sothat property (1) comprises the largest component of the current andproperty (2) comprises the smallest component of the current, orvice-versa. Accordingly, the CMO 110 comprises a mixed ionic electricconductor in that the current in memory cell 100 includes electron/holecurrent and ion current.

FIG. 6 depicts an example of arrayed memory cells according to variousembodiments of the invention. In this example, a memory cell 600includes a memory element 602, which, in turn, includes an electrolyticinsulator 670 and CMO material 680. Memory cell 600 further includes twoterminals 104 and 106. Terminals 104 and 106 can be electrically coupledwith or can be formed as electrodes 612 and 616. The electrodes (612,616) can be made from an electrically conductive material including butnot limited to, platinum (Pt), gold (Au), silver (Ag), iridium (Ir),iridium oxide (IrO_(X)), ruthenium (Ru), palladium (Pd), aluminum (Al),and the like.

In at least some embodiments, memory cell 600 can include a non-ohmicdevice (NOD) 614, which, in turn, can be formed on the memory element602 (e.g., either above or below memory element 602). NOD 614 can be a“metal-insulator-metal”(MIM) structure that includes one or more layersof electronically insulating material that are in contact with oneanother and sandwiched between metal layers (e.g., electrodes), or NOD614 can be a pair of diodes connected in a back-to-back configuration.U.S. Pat. No. 7,995,371, issued on Aug. 9, 2011, and titled “ThresholdDevice For A Memory Array” and U.S. Pat. No. 7,884,349, issued on Feb.8, 2011, and titled “Selection Device for Re-Writable Memory” are bothhereby incorporated by reference in their entirety and for all purposesand describe metal-insulator-metal and diode based non-ohmic devices.Memory cell 600 can be formed between conductive array lines, such asarray lines 692′ and 694′. Thus, memory cell 600 can be formed in anarray of other memory cells, the array can be a cross-point array 699including groups of conductive array lines 692 and 694. For example,array lines 692 can be electrically coupled with the electrodes 612 ofthe memory cells 600 and/or may be in contact with a surface 612 s ofthe electrodes 612 and array lines 694 can be electrically coupled withthe electrodes 616 of the memory cells 600 and/or may be in contact witha surface 616 s of the electrodes 616.

Moving now to FIGS. 6A and 6B, memory cells 600 include the non-ohmicdevice 614. The non-ohmic device 614 is electrically in series with thememory element 602 and the pair of electrodes (612, 616). As wasdiscussed above, each memory cell 600 stores data as a plurality ofconductivity profiles. Therefore, each memory element 602 can beschematically depicted as a resistor that is electrically in series withthe non-ohmic devices 614. A resistance at a certain voltage of aspecific memory element 602 is indicative of a value of stored data inthat memory element 602. As an example, each memory element 602 canstore a single bit of data as one of two distinct conductivity profileshaving a first resistive state R₀ at a read voltage V_(R) indicative ofa logic “0” and a second resistive state R₁ at V_(R) indicative of alogic “1”, where R₀≠R₁. Preferably, a change in conductivity, measuredat the read voltage V_(R), between R₀ and R₁ differs by a large enoughfactor so that a sense unit that is electrically coupled with the memoryelement 602 can distinguish the R₀ state from the R₁ state. For example,the factor can be at least a factor of approximately 5. Preferably, thepredetermined factor is approximately 10 or more (e.g., R₀≈1 MΩ andR₁≈100 kΩ). The larger the predetermined factor is, the easier it is todistinguish between resistive states R₀ and R₁. Furthermore, largepredetermined factors may also allow intermediate resistive states(e.g., R₀₀, R₀₁, R₁₀ and R₁₁).

The resistance of the memory element 602 may not be a linear function ofthe voltage applied across the memory element 602 at the electrodes(612, 616). Therefore, a resistance R_(S) of the memory elements 602 canapproximately be a function of the applied voltage V such thatR_(S)≈f(V). The applied voltage V can be a read voltage, a writevoltage, or a half-select voltage. Moreover, because the non-ohmicdevices 614 are electrically in series with their respective memoryelement 602, a resulting series resistance creates a voltage drop acrossthe non-ohmic devices 614 such that the actual voltage across the memoryelement 602 will be less than the voltage applied across the electrodes(612, 616). As one example, if the read voltage V_(R)≈3V and the voltagedrop across the non-ohmic devices 614 is approximately 2.0V, then aneffective read voltage across the memory element 602 is approximately1.0V.

The non-ohmic devices 614 create a non-linear I-V characteristic curvethat falls within a desired operational current-voltage range for dataoperations (e.g., read and write operations) to the memory element 602.The non-ohmic devices 614 substantially reduce or eliminate current flowwhen the memory element 602 is not selected for a read or writeoperation. The non-ohmic devices 614 allow data to be written to thememory element 602 when a write voltage V_(W) of appropriate magnitudeand polarity is applied across the electrodes (612, 616) of a selectedmemory element 602. Similarly, the non-ohmic devices 614 allow data tobe read from the memory element 602 when a read voltage V_(R) ofappropriate magnitude and polarity is applied across the electrodes(612, 616) of a selected memory element 602. An additional function ofthe non-ohmic devices 614 is to substantially reduce or eliminatecurrent flow through half-selected and un-selected memory elements 602.

The non-ohmic devices 614 may include a plurality of layers of thin filmmaterials that are in contact with one another and are denoted as n inFIGS. 6A and 6B. Those layers can include a pair of electrodes thatsandwich one or more layers of a dielectric material. The dielectricmaterial(s) are operative as a tunnel barrier layer(s) that generate thenon-linear I-V characteristic of the non-ohmic devices 614. As oneexample, the non-ohmic devices 614 can comprise a sandwich of Ptelectrode/TiO_(X) dielectric layer/Pt electrode. The thicknesses of thePt and TiO_(X) materials will be application dependent. The Ptelectrodes may have a thickness in a range from about 500 Å to about 100Å, for example. The TiO_(X) dielectric layer may have a thickness in arange from about 50 Å to about 10 Å, for example. Examples of suitablematerials for the dielectric layers for the non-ohmic devices 614include but are not limited to SiO₂, Al₂O₃, SiN_(X), HfSiO_(X),ZrSiO_(X), Y₂O₃, Gd₂O₃, LaAlO₃, HfO₂, ZrO₂, Ta₂O₅, TiO_(X),yttria-stabilized zirconia (YSZ), Cr₂O₃, and BaZrO₃. Suitable materialsfor the electrically conductive layers for the electrodes of thenon-ohmic devices 614 include but are not limited to metals (e.g.,aluminum Al, platinum Pt, palladium Pd, iridium Ir, gold Au, copper Cu,tantalum Ta, tantalum nitride TaN, titanium (Ti), and tungsten W), metalalloys, refractory metals and their alloys, and semiconductors (e.g.,silicon Si). Alternatively, the non-ohmic devices 614 can include a pairof diodes connected in a back-to-back configuration (not shown), forexample. Each of the diodes can be manufactured to only allow current toflow in a certain direction when its breakdown voltage (of apredetermined magnitude and polarity) is reached.

In FIG. 6A, the non-ohmic device 614 is positioned adjacent to electrode612; whereas, in FIG. 6B, the non-ohmic device 614 is positionedadjacent to electrode 616. In some applications, the material for thepair of electrodes (612, 616) will be compatible with the electrodematerial for the non-ohmic devices 614. In those applications, one ofthe pair of electrodes (612, 616) can serve as one of the electrodes forthe non-ohmic devices 614.

Reference is now made to FIG. 6C, where a portion of the cross-pointarray 699 includes a plurality of first conductive array lines 692 (oneis depicted) and a plurality of second conductive array lines 694 (oneis depicted), and a plurality memory cells 600 (one is depicted). Eachmemory cell 600 includes a first terminal 104 in electricalcommunication with only one of the first conductive array lines 692 anda second terminal 106 in electrical communication with only one of thesecond conductive array lines 694. Each memory cell 600 includes amemory element 602 that is electrically in series with the first andsecond terminals (104, 106). The first and second terminals (104, 106)can be the pair of electrodes (612, 616) described in reference to FIGS.6, 6A, and 6B. As depicted in FIG. 6C, the memory cell 600 may includethe above mentioned non-ohmic devices 614. The non-ohmic device 614 iselectrically in series with the first and second terminals (104, 106)and with the memory element 602. The position of the non-ohmic device614 in the memory cell 600 can be as depicted or the non-ohmic device614 can be positioned between the second terminal 106 and the memoryelement 602. Although, non-ohmic device 614 is depicted, the memory cell600 need not include a non-ohmic device 614 and the first terminal 104may be in contact with the memory element 602.

Although a coordinate system is not depicted, the first conductive arraylines 692 may be substantially aligned with an X-axis (e.g., runningfrom left to right on the drawing sheet) and the second conductive arraylines 694 may be substantially aligned with a Y-axis (e.g., looking intothe drawing sheet). The aforementioned read and write and voltages areapplied to a selected memory cell 600 by applying the voltages acrossthe two conductive array lines that the memory cell 600 is positionedbetween. In FIG. 6C, by applying the read and write and voltages acrossthe terminals (104, 106), stored data can be read from the selectedmemory cell 600 or new data can be written to the selected memory cell600. A read current I_(R) flows through the selected memory cell 600,the memory element 602, and the non-ohmic device 614, if it is includedin the memory cell 600. The direction of flow of the read current I_(R)(e.g., substantially along a Z-axis) will depend on the polarity of theread voltage. For example, if a positive read voltage potential isapplied to terminal 104 and a negative read voltage potential is appliedto the terminal 106, then the read current I_(R) will flow from thefirst conductive array line 692 to the second conductive array line 694.In some applications, the memory cell 600 comprises the smallestrepeatable unit that makes up the array 699 and may include all or aportion of the conductive array lines (692, 694) as denoted by thedashed line for the memory cell 600. One skilled in the art willappreciate that a dielectric material such as silicon oxide (SiO_(X)),silicon nitride (SiN_(X)), or the like may be used to electricallyisolate adjacent memory cells 600 from one another and to fill in openareas within the array 699.

Attention is now directed to FIG. 6D, where the array 699 includes aplurality of memory cells 600. However, unlike the memory cell 600 ofFIG. 6C, where the memory element 602 comprises discrete (e.g., etched)layers for CMO 680 and electrolytic insulator 670 and those layers aresubstantially vertically aligned with other thin film layers (e.g., theelectrodes) in the memory cell 600, the memory cells 600 of FIG. 6Dcomprise continuous and unetched layers of material for the CMO 680 andelectrolytic insulator 670. In FIG. 6D, for each memory element 602(shown in dashed outline), portions 680 c of the CMO layer 680 that arepositioned substantially within the dashed outline for the memoryelement 602 are crystalline in structure and are electricallyconductive. In contrast, portions 680 a that are positionedsubstantially outside the dashed outline are amorphous in structure andare electrically insulating and may be referred to as insulating metaloxide (IMO) regions 680 a. The IMO regions 680 a electrically isolateadjacent memory cells 600 and their respective memory elements 602 fromone another. For example, when a read voltage is applied acrossterminals 104 and 106, the resulting read current I_(R) flows throughthe memory cell 600 on the left and does not electrically interact withthe memory cell 600 on the right due to the insulating properties of theIMO regions 680 a. The IMO regions 680 a can be formed by ionimplantation of portions of the CMO layer 680 during fabrication. Layersof thin film materials positioned above layer 670 may be used as animplantation mask operative to protect masked portions of the CMO layer680 from the implanted species. Portions of the CMO layer 680 that arenot protected by the mask are implanted and become the IMO regions 680a. One skilled in the art will appreciate that a dielectric materialsuch as silicon oxide (SiO_(X)), silicon nitride (SiN_(X)), or the likemay be used to electrically isolate adjacent memory cells 600 from oneanother and to fill in open areas within the array 699.

Turning now to FIG. 7, an integrated circuit 700 can includenon-volatile and re-writable memory cells 600 disposed in a single layer710 or in multiple layers 740 of memory, according to variousembodiments of the invention. In this example, integrated circuit 700 isshown to include either multiple layers 740 of memory (e.g., layers 742a, 742 b, . . . 742 n) or a single layer 710 of memory 712 formed on(e.g., fabricated above) a base layer 720 (e.g., a silicon wafer). In atleast some embodiments, each layer of memory (712, or 742 a, 742 b, . .. 742 n) can include the cross point array 699 having conductive arraylines (692, 694) arranged in different directions (e.g., substantiallyorthogonal to one another) to access memory cells 600 (e.g.,two-terminal memory cells). For example, conductors 692 can beX-direction array lines (e.g., row conductors) and conductors 694 can beY-direction array lines (e.g., column conductors). Base layer 720 caninclude a bulk semiconductor substrate upon which circuitry, such asmemory access circuits (e.g., address decoders, drivers, sense amps,etc.) can be formed. For example, base layer 720 may be a silicon (Si)substrate upon which the active circuitry 730 is fabricated. The activecircuitry 730 includes analog and digital circuits configured to performdata operations on the memory layer(s) that are fabricated above thebase layer 720. An interconnect structure (not shown) including vias,plugs, thrus, and the like, may be used to electrically communicatesignals from the active circuitry 730 to the conductive array lines(692, 694).

Reference is now made to FIG. 8A, where integrated circuit 700 includesthe base layer 720 and active circuitry 730 fabricated on the base layer720. As one example, the base layer 720 can be a silicon (Si) wafer andthe active circuitry 730 can be microelectronic devices formed on thebase layer 720 using a CMOS fabrication process. The memory cells 600and their respective conductive array lines (692, 694) can be fabricatedon top of the active circuitry 730 in the base layer 720. Those skilledin the art will appreciate that an inter-level interconnect structure(not shown) can electrically couple the conductive array lines (692,694) with the active circuitry 730 which may include several metallayers. For example, vias can be used to electrically couple theconductive array lines (692, 694) with the active circuitry 730. Theactive circuitry 730 may include but is not limited to address decoders,sense amps, memory controllers, data buffers, direct memory access (DMA)circuits, voltage sources for generating the read and write voltages,just to name a few. Active circuits 810-818 can be configured to applythe select voltage potentials (e.g., read and write voltage potentials)to selected conductive array lines (692′, 694′). Moreover, the activecircuitry 730 may be coupled with the conductive array lines (692′,694′) to sense the read current I_(R) from selected memory cells 600′during a read operation and the sensed current can be processed by theactive circuitry 730 to determine the conductivity profiles (e.g., theresistive state) of the selected memory cells 600′. In someapplications, it may be desirable to prevent un-selected array lines(692, 694) from floating. The active circuits 730 can be configured toapply an un-select voltage potential (e.g., approximately a groundpotential) to the un-selected array lines (692, 694). A dielectricmaterial 811 (e.g., SiO₂) may be used where necessary to provideelectrical insulation between elements of the integrated circuit 700.

Moving now to FIG. 8B, an integrated circuit 820 includes a plurality ofnon-volatile memory arrays that are vertically stacked above one another(e.g., along the Z-axis) and are positioned above the base layer 720that includes the active circuitry 730. The integrated circuit 820includes vertically stacked memory layers A and B and may includeadditional memory layers up to an nth memory layer. The memory layers A,B, . . . through the nth layer can be electrically coupled with theactive circuitry 730 in the base layer 720 by an inter-levelinterconnect structure as was described above. Layer A includes memorycells 600 a and first and second conductive array lines (692 a, 694 a),Layer B includes memory cells 600 b and first and second conductivearray lines (692 b, 694 b), and if the nth layer is implemented, thenthe nth layer includes memory cells 600 n and first and secondconductive array lines (692 n, 694 n). Dielectric materials 825 a, 825b, and 825 n (e.g., SiO₂) may be used where necessary to provideelectrical insulation between the memory layers of the integratedcircuit 820. Active circuits 840-857 can be configured to apply theselect voltage potentials (e.g., read and write voltage potentials) toselected conductive array lines (e.g., 692 a, b, . . . n, and 694 a, b,. . . n). Driver circuits 850 and 857 are activated to select conductivearray lines 692′ and 694′ to select memory cell 600 b′ for a dataoperation. As was described above, the active circuits 730 can be usedto sense the read current I_(R) from selected memory cells 600 b′ duringa read operation and can be configured to apply the un-select voltagepotential to the un-selected array lines.

Attention is now directed to FIG. 8C, where a vertically stacked array830 includes a plurality of memory layers A, B, C, and D with eachmemory layer including memory cells 600 a, 600 b, 600 c, and 600 d.Although only four layers are depicted, the array 830 can includeadditional layers up to an nth layer. The array 830 includes two levelsof x-direction conductive array lines 692 a and 692 b, and three levelsof y-direction conductive array lines 694 a, 694 b, and 694 c. Incontrast to the integrated circuit 820 depicted in FIG. 8B where eacharray layer is electrically isolated from other layers by a dielectricmaterial, each memory cell 600 a, 600 b, 600 c, and 600 d shares aconductive array line with other memory cells that are positioned above,below, or both above and below that memory cell. Conductive array lines692 a′ and 694 a′ select a memory cell 600 a′ for a data operation, andconductive array lines 692 b′ and 694 c′ select a memory cell 600 d′ fora data operation (see FIG. 8D).

In FIG. 8D, an integrated circuit 840 includes base layer 720, activecircuitry 730, and vertically staked memory layers A, B, C, and D thatare fabricated above the base layer 720. Active circuits 840-857 areconfigured to perform data operations on the vertically staked memorylayers A, B, C, and D. Driver circuits 844 and 857 are activated toselect memory cell 600 a′ for a data operation and driver circuits 842and 848 are activated to select memory cell 600 d′ for a data operation.A dielectric layer 851 is operative to electrically isolate the variouscomponents of integrated circuit 840.

Moving on to FIG. 9, an exemplary memory system 900 includes theaforementioned non-volatile two-terminal cross-point memory array 700(array 700 hereinafter) and the plurality of first conductive and secondconductive traces denoted as 692 and 694, respectively. The memorysystem 900 also includes an address unit 903 and a sense unit 905. Theaddress unit 903 receives an address ADDR, decodes the address, andbased on the address, selects at least one of the plurality of firstconductive traces (denoted as 692′) and one of the plurality of secondconductive traces (denoted as 694′). The address unit 903 applies selectvoltage potentials (e.g., read or write voltages) to the selected firstand second conductive traces 692′ and 694′. The address unit 903 alsoapplies a non-select voltage potential to unselected traces 692 and 694.The sense unit 905 senses one or more currents flowing through one ormore of the conductive traces. During a read operation to the array 700,current sensed by the sense unit 905 is indicative of stored data in amemory cell 600′ positioned at an intersection of the selected first andsecond conductive traces 692′ and 694′. A bus 921 coupled with anaddress bus 923 can be used to communicate the address ADDR to theaddress unit 903. The sense unit 905 processes the one or more currentsand at least one additional signal to generate a data signal DOUT thatis indicative of the stored data in the memory plug. In someembodiments, the sense unit 905 may sense current flowing through aplurality of memory plugs and processes those currents along withadditional signals to generate a data signal DOUT for each of theplurality of memory plugs. A bus 927 communicates the data signal DOUTto a data bus 929. During a write operation to the array 700, theaddress unit 903 receives write data DIN to be written to a memory plugspecified by the address ADDR. A bus 925 communicates the write data DINfrom the data bus 929 to the address unit 903. The address unit 903determines a magnitude and polarity of the select voltage potentials tobe applied to the selected first and second conductive traces 692′ and694′ based on the value of the write data DIN. For example, onemagnitude and polarity can be used to write a logic “0” and a secondmagnitude and polarity can be used to write a logic “1”. In otherembodiments, the memory system 900 can include dedicated circuitry thatis separate from the address unit 903 to generate the select potentialsand to determine the magnitude and polarity of the select potentials.

One skilled in the art will appreciate that the memory system 900 andits components (e.g., 903 and 905) can be electrically coupled with andcontrolled by an external system or device (e.g., a microprocessor or amemory controller). Optionally, the memory system 900 can include atleast one control unit 907 operative to coordinate and control operationof the address and sense units 903 and 905 and any other circuitrynecessary for data operations (e.g., read and write operations) to thearray 700. One or more signal lines 909 and 911 can electrically couplethe control unit 907 with the address and sense units 903 and 905. Thecontrol unit 907 can be electrically coupled with an external system(e.g., a microprocessor or a memory controller) through one or moresignal lines 913.

As was described above in reference to FIGS. 7 through 8D, one or moreof the arrays 700 can be positioned (e.g., fabricated BEOL) over asubstrate 720 that includes active circuitry 730 and the activecircuitry 730 can be electrically coupled with the array(s) 700 using aninterconnect structure that couples signals from the active circuitry730 with the conductive array lines 692 and 694. In FIG. 9, the busses,signal lines, control signals, the address, sense, and control units903, 905, and 907 can comprise the active circuitry 730 and its relatedinterconnect, and can be fabricated FEOL on the substrate 720 (e.g., asilicon wafer) using a microelectronics fabrication technology, such asCMOS, for example.

Reference is now made to FIG. 10, where an electrical system 1000includes a CPU 1001 that is electrically coupled 1004 with a bus 1002,an I/O unit 1007 that is electrically coupled 1010 with the bus 1002,and a storage unit 1005 that is electrically coupled 1008 with the bus1002. The I/O unit 1007 is electrically coupled 1012 to external sources(not shown) of input data and output data. The CPU 1001 can be any typeof processing unit including but not limited to a microprocessor (μP), amicro-controller (μC), and a digital signal processor (DSP), forexample. Via the bus 1002, the CPU 1001, and optionally the I/O unit1007, performs data operations (e.g., reading and writing data) on thestorage unit 1005. The storage unit 1005 stores at least a portion ofthe data in the aforementioned non-volatile two-terminal cross-pointarray as depicted in FIGS. 7 through 8D. Each memory array includes aplurality of the two-terminal memory cells 600. The configuration of thestorage unit 1005 will be application specific. Example configurationsinclude but are not limited to one or more single layer non-volatiletwo-terminal cross-point arrays (e.g., 712) and one or more verticallystacked non-volatile two-terminal cross-point arrays (e.g., 742 a-742n). In the electrical system 1000, data stored in the storage unit 1005is retained in the absence of electrical power. The CPU 1001 may includea memory controller (not shown) for controlling data operations to thestorage unit 1005.

Alternatively, the electrical system 1000 may include the CPU 1001 andthe I/O unit 1007 coupled with the bus 1002, and a memory unit 1003 thatis directly coupled 1006 with the CPU 1001. The memory unit 1003 isconfigured to serve some or all of the memory needs of the CPU 1001. TheCPU 1001, and optionally the I/O unit 1007, executes data operations(e.g., reading and writing data) to the non-volatile memory unit 1003.The memory unit 1003 stores at least a portion of the data in theaforementioned non-volatile two-terminal cross-point array as depictedin FIGS. 7A through 8D. Each memory array includes a plurality of thetwo-terminal memory elements 120. The configuration of the memory unit1003 will be application specific. Example configurations include butare not limited to one or more single layer non-volatile two-terminalcross-point arrays (e.g., 712) and one or more vertically stackednon-volatile two-terminal cross-point arrays (e.g., 742 a-742 n). In theelectrical system 1000, data stored in the memory unit 1003 is retainedin the absence of electrical power. Data and program instructions foruse by the CPU 1001 may be stored in the memory unit 1003. The CPU 1001may include a memory controller (not shown) for controlling dataoperations to the non-volatile memory unit 1003. The memory controllermay be configured for direct memory access (DMA).

Reference is now made to FIG. 11, where a top plan view depicts a singlewafer (denoted as 1170 and 1170′) at two different stages offabrication: FEOL processing on the wafer denoted as 1170 during theFEOL stage of processing where active circuitry 730 is formed; followedby BEOL processing on the same wafer denoted as 1170′ during the BEOLstage of processing where one or more layers of non-volatile memory areformed. Wafer 1170 includes a plurality of the base layer die 720 (see720 in FIG. 7) formed individually on wafer 1170 as part of the FEOLprocess. As part of the FEOL processing, the base layer die 720 may betested 1172 to determine their electrical characteristics,functionality, performance grading, etc. After all FEOL processes havebeen completed, the wafer 1170 is optionally transported 1104 forsubsequent BEOL processing (e.g., adding one or more layers of memorysuch as single layer 712 or multiple layers 742 a, 742 b, . . . 742 n)directly on top of each base layer die 720. A base layer die 720 isdepicted in cross-sectional view along a dashed line FF-FF where thesubstrate the die 720 is fabricated on (e.g., a silicon Si wafer) andits associated active circuitry 730 are positioned along the −Z axis.For example, the one or more layers of memory are grown directly on topof an upper surface 720 s of each base layer die 720 as part of thesubsequent BEOL processing.

During BEOL processing the wafer 1170 is denoted as wafer 1170′, whichis the same wafer subjected to additional processing to fabricate thememory layer(s) directly on top of the base layer die 720. Base layerdie 720 that failed testing may be identified either visually (e.g., bymarking) or electronically (e.g., in a file, database, email, etc.) andcommunicated to the BEOL fabricator and/or fabrication facility.Similarly, performance graded base layer die 720 (e.g., graded as tofrequency of operation) may identified and communicated to BEOL thefabricator and/or fabrication facility. In some applications the FEOLand BEOL processing can be done by the same fabricator or performed atthe same fabrication facility. Accordingly, the transport 1104 may notbe necessary and the wafer 1170 can continue to be processed as thewafer 1170′. The BEOL process forms the aforementioned memory layer(s)directly on top of the base layer die 720 to form a finished die 800(see die 800 in FIGS. 8A, 8B, and 8D) that includes the FEOL circuitryportion 720 along the −Z axis and the BEOL memory portion along the +Zaxis (see FIGS. 8A-8D). A cross-sectional view along a dashed line BB-BBdepicts a memory device die 800 with a single layer of memory 712 grown(e.g., fabricated) directly on top of base die 720 along the +Z axis,and alternatively, another memory device die 800 with three verticallystacked layers of memory 742 a, 742 b, and 742 c grown (e.g.,fabricated) directly on top of base die 720 along the +Z. Finished die800 on wafer 1170′ may be tested 1174 and good and/or bad dieidentified. Subsequently, the wafer 1170′ can be singulated 1178 toremove die 800 (e.g., die 800 are precision cut or sawed from wafer1170′) to form individual memory device die 800. The singulated die 800may subsequently be packaged 1179 to form integrated circuits 1190 formounting to a PC board or the like, as a component in an electricalsystem (not shown). Here a package 1181 can include an interconnectstructure 1187 (e.g., pins, solder balls, or solder bumps) and the die800 mounted in the package 1181 and electrically coupled 1183 with theinterconnect structure 1187 (e.g., using wire bonding). The integratedcircuits 1190 (IC 1190 hereinafter) may undergo additional testing 1185to ensure functionality and yield. One or more of the IC's 1190 can beused in a data storage system such as an embedded memory system (e.g.,portable PC's, cell phones, PDA's, image capture devices, portable gameplayers, MP3 players, video players, etc.), a RAID storage system inwhich the non-volatile memory in the one or more layers of memory ineach IC 1190 is used to replace or supplant hard disc drives (HDD's) inthe RAID system. Unlike conventional FLASH non-volatile memory, the IC's1190 do not require an erase operation prior to a write operation so thelatency associated with the erase operation is eliminated and thelatency associated with FLASH OS and/or FLASH file system required formanaging the erase operation is eliminated. Another application for theIC's 1190 is as a replacement for conventional FLASH-based non-volatilememory in solid state drives (SSD's). Here, one or more of the IC's 1190can be mounted to a PC board along with other circuitry and placed in anappropriate enclosure to implement a SSD that can be used to replace aHDD. As mentioned above, the IC's 1190 do not require the erase beforewrite operation and it associated latency and overhead. For both RAIDand SSD applications, the vertically stacked memory arrays allow forincreases in storage density without increasing die size because thememory arrays are fabricated above their associated active circuitry soextra memory capacity can be achieved by adding additional layers ofmemory above the FEOL base layer die 720.

The various embodiments of the invention can be implemented in numerousways, including as a system, a process, an apparatus, or a series ofprogram instructions on a computer readable medium such as a computerreadable storage medium or a computer network where the programinstructions are sent over optical or electronic communication links. Ingeneral, the steps of disclosed processes can be performed in anarbitrary order, unless otherwise provided in the claims.

The foregoing description, for purposes of explanation, uses specificnomenclature to provide a thorough understanding of the invention.However, it will be apparent to one skilled in the art that specificdetails are not required in order to practice the invention. In fact,this description should not be read to limit any feature or aspect ofthe present invention to any embodiment; rather features and aspects ofone embodiment can readily be interchanged with other embodiments.Notably, not every benefit described herein need be realized by eachembodiment of the present invention; rather any specific embodiment canprovide one or more of the advantages discussed above. In the claims,elements and/or operations do not imply any particular order ofoperation, unless explicitly stated in the claims. It is intended thatthe following claims and their equivalents define the scope of theinvention.

1. A memory device, comprising: a first terminal structure; a second terminal structure; and a re-writeable non-volatile two-terminal memory element directly electrically in series with the first and second terminal structures and operative to store at least one-bit of data as a plurality of conductivity profiles that are retained in the absence of electrical power, the memory element including a tunnel barrier layer in contact with the first terminal structure and including a first thickness, and a conductive binary oxide material including mobile oxygen ions and having a form A_(X)O_(Y), where O represents oxygen and A represents a metal, the conductive binary oxide material is in contact with the tunnel barrier layer and with the second terminal structure.
 2. The memory device of claim 1, wherein the conductive binary oxide material comprises tin oxide.
 3. The memory device of claim 1, wherein the conductive binary oxide material comprises zinc oxide.
 4. The memory device of claim 1, wherein the conductive binary oxide material comprises a doped titanium oxide.
 5. The memory device of claim 4, wherein the titanium oxide is doped with niobium.
 6. The memory device of claim 1, wherein the tunnel barrier layer includes vacancies operative to reversibly receive a portion of the mobile oxygen ions in response to a write voltage applied across the first and second terminal structures.
 7. The memory device of claim 6, wherein the tunnel barrier layer is an electrolyte to the mobile oxygen ions and is permeable to the mobile oxygen ions when the write voltage is applied.
 8. The memory device of claim 1, wherein the first thickness is approximately 35 Å or less.
 9. The memory device of claim 1, wherein the tunnel barrier layer comprises a material selected from the group consisting of a rare earth oxide, a rare earth metal oxide, yttria stabilized zirconia (YSZ), zirconium oxide, yttrium oxide, hafnium oxide, gadolinium oxide, and erbium oxide.
 10. The memory device of claim 1, wherein the conductive binary oxide material includes a structure selected from the group consisting of an amorphous structure, a single crystalline structure, a polycrystalline structure, a multi-phase crystalline structure, a mixed-phase crystalline structure, a columnar crystalline structure, and a micro-crystalline structure.
 11. The memory device of claim 1 and further comprising: a non-ohmic device electrically in series with the memory element and with the first and second terminal structures.
 12. The memory device of claim 1, wherein the first terminal structure is electrically coupled with only one of a plurality of first conductive array lines in a two-terminal cross-point memory array and the second terminal structure is electrically coupled with only one of a plurality of second conductive array lines in the two-terminal cross-point memory array.
 13. The memory device of claim 12, wherein the two-terminal cross-point memory array is connected with and is positioned above a substrate including active circuitry electrically coupled with the plurality of first and second conductive array lines and operative to perform data operation on the two-terminal cross-point memory array.
 14. The memory device of claim 1, wherein the first thickness is configured for electron tunneling when a voltage for data operations is applied across the first and second terminal structures.
 15. The memory device of claim 1, wherein the conductive binary oxide material is doped.
 16. The memory device of claim 1, wherein the tunnel barrier layer, the conductive binary oxide material or both are deposited in whole or in part using atomic layer deposition (ALD).
 17. A memory device, comprising: a first terminal structure; a second terminal structure; and a re-writeable non-volatile two-terminal memory element directly electrically in series with the first and second terminal structures and operative to store at least one-bit of data as a plurality of conductivity profiles that are retained in the absence of electrical power, the memory element including a tunnel barrier layer in contact with the first terminal structure and including a first thickness, and a conductive metal oxide (CMO) including mobile oxygen ions and made from a Ruddlesden-Popper material, the CMO is in contact with the tunnel barrier layer and with the second terminal structure.
 18. The memory device of claim 17, wherein the Ruddlesden-Popper material includes a form ABO₃, where O represents oxygen, A represents an alkaline earth metal element, and B represents a transition metal element.
 19. The memory device of claim 17, wherein the Ruddlesden-Popper material includes a form AO(ABO₃)n, where O represents oxygen, A represents at least one alkaline earth metal element, B represents at least one transition metal element, and n represents a Ruddlesden-Popper phase.
 20. The memory device of claim 17, wherein the tunnel barrier layer comprises a material selected from the group consisting of a rare earth oxide, a rare earth metal oxide, yttria stabilized zirconia (YSZ), zirconium oxide, yttrium oxide, hafnium oxide, gadolinium oxide, and erbium oxide.
 21. The memory device of claim 17 and further comprising: a non-ohmic device electrically in series with the memory element and with the first and second terminal structures.
 22. The memory device of claim 17, wherein the Ruddlesden-Popper material includes a structure selected from the group consisting of an amorphous structure, a single crystalline structure, a polycrystalline structure, a multi-phase crystalline structure, a mixed-phase crystalline structure, a columnar crystalline structure, and a micro-crystalline structure.
 23. The memory device of claim 17, wherein the tunnel barrier layer, the Ruddlesden-Popper material or both are deposited in whole or in part using atomic layer deposition (ALD).
 24. The memory device of claim 17, wherein the first thickness is configured for electron tunneling when a voltage for data operations is applied across the first and second terminal structures.
 25. A memory device, comprising: a first terminal structure; a second terminal structure; and a re-writeable non-volatile two-terminal memory element directly electrically in series with the first and second terminal structures and operative to store at least one-bit of data as a plurality of conductivity profiles that are retained in the absence of electrical power, the memory element including a tunnel barrier layer in contact with the first terminal structure and including a first thickness, and a conductive metal oxide (CMO) including mobile oxygen ions and made from a multiple B-site perovskite material including a plurality of perovskite unit cells, the CMO is in contact with the tunnel barrier layer and with the second terminal structure, the multiple B-site perovskite material includes a form A_(X)(B₁,B₂)_(Y)O_(Z), where A_(X) represents one or more elements selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, calcium, strontium, and barium that are positioned at A-sites in the plurality of perovskite unit cells, B₁ represents a first transition metal element positioned at B-sites in a first portion of the plurality of perovskite unit cells, B₂ represents a second transition metal element positioned at B-sites in a second portion of the plurality of perovskite unit cells, the second transition metal element is different than the first transition metal element, where O represents oxygen, where X can be any number, where Y is typically 1, and where Z is typically
 3. 26. The memory device of claim 25, wherein the tunnel barrier layer comprises a material selected from the group consisting of a rare earth oxide, a rare earth metal oxide, yttria stabilized zirconia (YSZ), zirconium oxide, yttrium oxide, hafnium oxide, gadolinium oxide, and erbium oxide.
 27. The memory device of claim 25 and further comprising: a non-ohmic device electrically in series with the memory element and with the first and second terminal structures.
 28. The memory device of claim 25, wherein the multiple B-site perovskite material includes a structure selected from the group consisting of an amorphous structure, a single crystalline structure, a polycrystalline structure, a multi-phase crystalline structure, a mixed-phase crystalline structure, a columnar crystalline structure, and a micro-crystalline structure.
 29. The memory device of claim 25, wherein the tunnel barrier layer, the multiple B-site perovskite material or both are deposited in whole or in part using atomic layer deposition (ALD).
 30. The memory device of claim 25, wherein the first thickness is configured for electron tunneling when a voltage for data operations is applied across the first and second terminal structures. 